ALE is geared towards mesh terrains, you can export a heightmap but the best looking textures go with the mesh export (.b3d). You can also load objects onto the terrain, position, and export a "prop file" Lightmapping is great and includes the objects..so the house you plop down cast shadows on the terrain..nice bonus. You can scale the texture so that it looks highly detailed when close up.

TerraED is loaded with a lot of features, but as Falelorn said it slows down the more objects you place/ load in. Also consider the terrain is made by painting colors (not textures) onto the landscape, then tiling a high res detail texture over the terrain. This does look really nice, but you won't be able to use textures. (If you want to try this method out for free, try TotalTerrain in the toolbox. Paint a colormap, then when you load a terrain in blitz, texture layer 2 with a detail texture)

T.ED looks very promising, it can do both methods above..the only thing lacking is the object import but the author stated it's coming. The interface is pretty slick and easy to use, and it's fast as well. The other two are not actively being worked, wheras T.ED seems to get updates every other week or so (it's also the newest of the three)